Using tkinter to watch for clipboard,what's wr

Question

Some description about the code:

1. This is part of my program and I only put the related lines here
2. What I hope these code could do,is to watch for my clipboard.If I copy "http:xxx" to my clipboard,it shows a pop-up window.If the content of the clipboard doesn't change,the window won't show again
3. When running,it can pop up the window normally for one time,but won't do it again when I copy another string to clipboard starting with 'http:'
4. I've tried some different interval values in the after method,same result.

Code:

from tkinter import *
import os
import tkinter.messagebox as messagebox
import threading
import re

def watch_clipboard(tk,pipeout):  
    content = '' 
    last_content = ''
    while True:
        try:
            content = tk.clipboard_get()
        except TclError:
            pass
        result = re.match('http:',content)
        if content != last_content:
            if result:
                last_content = content
                message = 'show'.encode()    
                os.write(pipeout,message)


class GUI:
    def __init__(self):
        self.tk = Tk()
        self.tk.resizable(0, 0)
        self.tk.title('watch clipboard')
        pipein,pipeout = os.pipe()
        threading.Thread(target=watch_clipboard,daemon=True,args=(self.tk,pipeout)).start()
        self.tk.after(5000,lambda:self.clipboard_confirm(pipein))
        self.tk.mainloop()

    def clipboard_confirm(self,pipein):
        message = os.read(pipein,16)
        if message == b'show':
            self.tk.clipboard_clear()
            messagebox.askokcancel('', 'add this in?', default='ok')
            self.tk.after(5000,clipboard_confirm(pipein))   #add this


if __name__ == '__main__':
    gui = GUI()

EDIT:A. Rodas's code works.It seems that multithreading causes the problem.Deep reason remain unknown.

Answer 1

There's a good chance the problem is related to using threads -- calling Tkinter functions from anywhere other than the main thread can cause problems.

Is there a reason you're using a thread rather than takingbadvantage of the built-in infinite loop (the event loop)? I would advise making use of after to check the keyboard every second or so.

Answer 2

I think multithreading isn't the best approach for your situation and after may be enough. Instead of a busy waiting loop, you can call tk.after with a lower timeout. Then you just need to move the logic of watch_clipboard to your class, so you don't have to worry about the communication between the threads.

class GUI:
    def __init__(self):
        self.tk = Tk()
        self.tk.resizable(0, 0)
        self.tk.title('watch clipboard')
        self.last_content = ''
        self.tk.after(100, self.watch_clipboard)
        self.tk.mainloop()
    def watch_clipboard(self):
        try:
            content = self.tk.clipboard_get()
            if content != self.last_content and content.startswith('http:'):
                self.last_content = content
                self.tk.clipboard_clear()
                messagebox.askokcancel('', 'add this in?', default='ok')
        except TclError:
            pass
        self.tk.after(100, self.watch_clipboard)

Answer 3

@laike9m
The error with your code is that os.pipe is used.
Os.read() is a blocking function that will receive os.read() blocking once clipboard_confirm is run. Causes the UI to get stuck.
This bug has nothing to do with after and multithreading.